Converters are commonly used in many of today's electronic equipment for converting a supply voltage to an output voltage. Important performance factors for such converters are output voltage ripples and noises. One conventional technique utilizes a boost circuit in the converters. The boost circuits may have a low voltage ripple and low noise. However, such boost circuits typically have a right-hand zero in their transfer functions in a continuous current mode, and thus resulting in poor performance in transient load response.
Another conventional technique for improving the converter performance is discussed in the thesis named “A Novel Voltage-boosting Converter: KY Converter.” FIG. 1 is a schematic diagram showing a topology of the KY converter. As shown in FIG. 1, the KY converter includes an input supply VIN, a switch M1 with a body diode D1, a switch M2 with a body diode D2, a diode D, an inductor L, capacitors C and Cb, and a load R interconnected with one another.
In operation, when the switch M1 is turned off and the switch M2 is turned on, the input supply VIN, the diode D, the capacitor Cb, and the switch M2 form a current loop. The input supply VIN provides power to the capacitor Cb, causing the voltage across the capacitor Cb to reach VIN. Also, the input supply VIN, the diode D, the inductor L, the capacitor C, and the load form a current loop as well. The input supply VIN provides power to the load R, as shown in FIG. 2(a). When the switch M1 is turned on and the switch M2 is turned off, the input supply VIN, the switch M1, the capacitor Cb, the inductor L, the capacitor C, and the load R form a current loop. The input supply VIN and the capacitor Cb provide power to the load R, as shown in FIG. 2(b).
Even though the KY converter can have a low-ripple output voltage, a good noise rejection, and a fast load response, according to the thesis, the KY converter has a few drawbacks. For example, the output voltage VO is in the range of VIN˜2*VIN, so the KY converter can only function as a step-up, but not a step-down converter. In addition, when switches M1 and M2 are both turned off or inoperative, the input supply VIN still supplies power to the load R through another current loop formed by the input supply VIN, the diode D, the inductor L, the capacitor C, and the load R. Thus the input voltage VIN and the output voltage VO can not be decoupled.